Plants get sunburned, too, so plan to shade some edibles from the sun. From seeds that refuse to germinate in soil temperatures above 85 degrees, to lettuces and greens that bolt and beans that wither, heat can destroy crops, stop fruit production and invite disease.
When nighttime temperatures remain above 75 degrees, tomato blossoms don’t pollinate and drop off plants. As temperatures rise, tomatoes and other vegetables can develop sun scald, a gray scab on skins. And, tomato skins may split.
Some do like it hot. Melons, peppers and corn thrive in the heat, which makes them grow faster and bigger.
Steps You Can Take to Keep Plants Cool:
- Mulch well. A 2-4” layer of mulch keeps plant roots cool and retains water. Be sure to use a light, natural-colored mulch instead of dark or dyed mulch.
- Water early or late. Watering in the early morning, before the heat of the day, is best and prevents heat scald on your plants and rapid evaporation. A second watering may be needed in the early evening if heat is extreme.
- Locate new transplants and seedlings in the shadow of taller plants. Look for opportunities to place smaller plants beside taller plants that provide partial shade.
- Train tomatoes to a cage. Simply growing upright in the cage allows leaves to provide shade for the tomatoes. If sun and heat are extreme, draping a layer of cheesecloth over the cages adds some protection.
- Protect large beds with hoops covered with shade cloth at least 12” above plants to lower air temperatures up to 15 degrees. For small areas, stretch shade cloth over tall stakes. Repurpose old window screens by staking them 12” above plants.
- Plant greens, lettuces, bush beans and broccoli in spots where they get only morning sun and afternoon shade to keep them from bolting, or going to seed, so you can harvest longer into the season.
Heat makes lettuce bitter. If this happens, pick and rinse leaves with cool water, wrap in a paper towel and refrigerate overnight; the bitterness will disappear.